Field of the Invention
This invention relates to removal of sulfur from a hydrocarbon material. More particularly, this invention relates to the use of a manganese-containing material in the removal of sulfur from hydrocarbon materials and subjecting the resulting reduced sulfur-containing hydrocarbon feedstock to hydrocarbon reforming.
Catalytic hydrocarbon reforming, a method to improve the octane value of a naphtha feedstock, is well known. Many of the catalysts used to carry out such a reforming process tend to be especially sulfur sensitive. Examples of such especially sulfur sensitive reforming catalysts are those employing a platinum-group metal, e.g., platinum, and optionally as a co-metal component, rhenium. Several examples of reforming processes are fixed-bed hydroforming (Standard Oil Development Company, M. W. Kellogg Company, and Standard Oil Company (Indiana)), Platforming (Universal Oil Products Company), Catforming (Atlantic Refining Company), Houdriforming (Houdry Process Corporation), Ultraforming (Standard Oil Company (Indiana)), Rexforming (Universal Oil Products Company), Powerforming (Esso Research and Engineering Company), Magnaforming (Engelhard Minerals and Chemicals Corporation), and Rheniforming (Chevron Research Company).
Under the high hydrogen partial pressure condition used in catalytic reforming, sulfur compounds are readily converted into hydrogen sulfide which, unless removed, will build up to a high concentration in hydrogen recycle gas. It becomes especially important in view of the high sulfur sensitivity of platinum-group metal reforming catalysts to use feedstocks having reduced sulfur levels, e.g. of less than about 1 ppm. "Reforming" is meant herein and in the claims to be a catalytic process wherein a hydrocarbon feedstock is contacted with a hydrocarbon reforming catalyst in the presence of hydrogen at hydrocarbon reforming conditions to produce at least one reformate product having an increased octane value, e.g., Research Octane Number (RON) relative to that of the hydrocarbon feedstock.
K. E. Louder et al. U.S. Pat. No. 3,898,153 (1975) disclose an improvement in catalytic reforming of naphthas wherein a hydrotreated feedstock is passed through a zinc oxide bed preceded by a chloride scavenging zone. The chloride scavenging zone is necessary because hydrochloric acid gas in the reformer recycle gas reacts with zinc oxide to form zinc chloride. The zinc chloride in turn is carried into the reforming zone where it adversely affects the reforming catalyst
P. R. Westmoreland et al. in Environmental Science and Technology, Volume 11, Pages 488-491, report initial rates for reaction between H.sub.2 S in a mixture of H.sub.2 S and H.sub.2 and MnO, CaO, ZnO and V.sub.2 O.sub.3 over a temperature range of 570.degree.-1470.degree. F. (300.degree.-800.degree. C.). Manganous oxide was reported to have the highest reaction rate and possessed favorable properties for a high temperature desulfurization process.
Removal of sulfur, either from waste gas or industrial exhaust or flue gases, by means of an oxide of manganese is disclosed in the following patents: U.S. Pat. Nos. 3,761,570 (1973), 3,723,598 (1973), 3,492,083 (1970) and British Pat. No. 1,144,071.
Removal of sulfur from carbonaceous solid fuels by conversion of sulfur impurities to hydrogen sulfide followed by absorption of the hydrogen sulfide on supported manganese oxide is disclosed in the following U.S. Pat. Nos. 2,927,063 (1960), 2,950,229 (1960), 2,950,231 (1960), and 3,101,303 (1963).
Methods for regenerating manganous oxide are disclosed in the following U.S. Pat. Nos. 2,927,063 (1960), 2,950,229 (1960), 3,492,083 (1970) and 3,101,303 (1963).
U.S. Pat. No. 4,045,331 (1977) discloses a process for both demetalization and desulfurization of a petroleum feedstock by means of a manganese oxide supported on an alumina.
U.S. Pat. No. 3,063,936 (1962) discloses removal of H.sub.2 S produced during a catalytic hydrodesulfurization of a naphtha fraction by contacting the hydrotreated feedstock in the vapor phase at about 662.degree. F. (350.degree. C.) with an absorbing material comprising zinc oxide (reported to be preferred), manganese oxide or iron oxide. The desulfurized naphtha is then used in a steam-reforming process for the production of methanol synthesis gases.
U.S. Pat. Nos. 1,840,158 (1932), 2,177,343 (1939), 2,618,586 (1952), 2,314,576 (1943), 2,950,229 (1960), 3,320,157 (1967), and 3,996,130 (1976) all disclose the use of a manganese-containing material to remove at least a portion of a sulfur component contained in a hydrocarbon material. However, none of these references disclose the removal of a sulfur component from a hydrocarbon material in the context of a reforming process. None of the references teach that sufficient removal of sulfur from the hydrocarbon material can be achieved so as to make them useful as feedstocks for a reforming zone. In summary, a teaching that the sulfur content of a hydrocarbon material can be reduced by means of a process employing a manganese-containing composition does not disclose nor teach that such removal is necessarily sufficient to permit use of such a process upstream from a reforming zone.
U.S. Pat. No. 4,155,835 (1979) discloses a process for desulfurizing a naphtha or other hydrocarbon fractions boiling below about 430.degree. F. which is accomplished by cascading such a sulfur-containing material with added hydrogen over a combination of desulfurizing catalyst, under appropriate process conditions, and thereafter passing the total effluent, over a massive catalyst comprising zinc oxide or other suitable metal oxides. A desulfurized effluent from the above process can then be again reformed with a by-mettalic catalyst. Other suitable metal oxides, other than zinc oxide, are broadly suggested, however, no specific examples of such other metal oxides are disclosed nor any criteria for selecting them.
Many of the cited references suggest that zinc ozide and manganese oxide are equally effective and can be used interchangeably. This teaching is misleading when halides are present. For example, none of the references teach or suggest that where halogen-containing compounds are present and can both contact and react with the material for removing sulfur, a means for scavenging halide, required in the case of zinc oxide, is not required in the case of manganese oxide. Halogen-containing compounds are often present in the hydrocarbon feedstock, the hydrogen recycle line, and/or the reforming zone due to addition of halogen-containing compounds into any and all of these in order to maintain the halogen content on a, e.g., platinum-group metal containing, reforming catalyst.
U.S. Pat. No. 2,922,756 (1960) discloses an endothermic reforming process for a sulfur-containing feedstock. Of critical importance to the invention disclosed in U.S. Pat. No. 2,922,756 is that a portion of the heat to carry out the endothermic process is derived from a heat transfer effected directly within the catalyst bed in a reaction zone. The selected material must have sufficient desulfurization qualities to remove sulfur in a moving bed configuration. Further, the material must be able to form a sulfide at specified conditions, but which will oxidize at other selected conditions in a heating zone and further be reduced by hydrogen or hydrocarbons. These materials must, of course, be heat retentive. Materials asserted to fulfill the above requirements include iron, nickel, cobalt, molybdenum, vanadium, manganese and mixtures thereof. That manganese can be used interchangeably and with equal effectiveness with the other cited materials in a moving or fluidized bed for the purpose of removing sulfur from a hydrocarbon material which is later to be reformed is a misleading teaching when applied to a fixed bed sulfur removal zone. It has been discovered that in a fixed bed configuration oxides of manganese perform in a surprisingly very superior fashion to the other oxides. The superior performance of oxides of manganese is discussed in more detail hereinafter.
As a reactant, manganous oxide has a significantly greater propensity than zinc oxide to absorb or react with hydrochloric acid under the following process conditions: temperature in the range 600.degree. to 1000.degree. F. (316.degree. to 538.degree. C.) preferably 650.degree. to 850.degree. F. (343.degree. to 454.degree. C.), pressure in the range 150-750 psig., a hydrogen concentration in the range 1/1 to 30/1 moles of hydrogen per mole of hydrocarbon, and a space velocity (vhsv) in the range 500-50,000 vol. of gas/hour/vol. of reactant.
It has been found that a manganese component, preferably a manganese oxide, will scavenge hydrogen sulfide significantly more effectively than zinc oxide as shown in Example 3. Further, it has been discovered surprisingly that unlike zinc oxide, manganese in the form of an oxide, halide or sulfide has a negligible, if any, adverse affect on a platinum-group metal reforming catalyst after an activation-regeneration cycle as shown in Example 5.
It has been discovered surprisingly that manganese oxide in the liquid phase has a superior ability to remove mercaptans from a hydrocarbon material than does zinc oxide in the liquid phase.
One difficulty with manganese-containing material for use in a sulfur removal zone is their tendency to give up hydrogen sulfide in the presence of water vapor. Clearly, the evolution of even small amounts of hydrogen sulfide, e.g., 3 ppm, can severely poison sensitive platinum-rhenium reforming catalysts. A source of such water vapor is often the recycled gas which leaves a reforming zone. We have found that liquid phase operation can permit easy isolation from such recycled gas as is shown in FIG. 2 at location E.